The present invention relates generally to devices and other apparatus useful in separating one material entrained in a slurry from the slurry transport fluid and finds particular use in a centrifugal dryer in preventing the aggregation against the screen of particulates entrained in the transport fluid, thus aiding in the drying of the particulates.
Centrifugal dryers are used to dry particulates carried by a transport fluid. A common use for them is the drying of plastic pellets entrained in a flow of water. An example of such a dryer is shown in U.S. Pat. No. 5,987,769 to Ackerman et al., which is also assigned to the present assignee of this application.
Centrifugal dryers typically include an upright rotatable rotor having a plurality of blades or paddles attached thereto and extending outwardly therefrom. Circumferentially disposed about the rotor is a screen with perforations small enough to prevent the desired particulates from passing therethrough and, preferably, from becoming lodged in the perforations. The rotor and screen are held within a shell. A slurry comprising a transport fluid, commonly water, and the desired particulates, such as newly formed plastic pellets, is introduced into the centrifugal dryer between the rotor and the screen at a slurry inlet closely adjacent to the bottom. As the slurry flows upwardly within the dryer, the transport fluid passes through the screen apertures whereas the particulates are trapped between the rotor and the screen. The blades engage the particulates and, desirably, xe2x80x9cbouncexe2x80x9d them back and forth between the screen and the rotor/blades, causing the pellets to dry as they move upwardly within the dryer to an outlet at the top of the dryer.
In operation of such centrifugal dryers, it has been found that the particulates will at times aggregate against the screen and will not in fact rebound between the screen and the rotating rotor with attached blades. The aggregated particulates tend to form a thin xe2x80x9csheetxe2x80x9d that embraces the screen and that is held there by the outward air and water flow created by the rotating rotor. Additionally, it has been found that the sheet will rotate around the inside circumference of the screen, though at a much slower rate than the rotation of the rotor itself. After a sufficient mass of particulates aggregate into the sheet, the sheet will collapse, with the particulates falling into the rotor causing a great noise and creating additional wear and tear on the dryer.
It would be desirable to have a centrifugal dryer that was not subject to the foregoing deficiencies and that would prevent the aggregation of particulates into a thin sheet lying against the inner surface of the screen.
It is an object of the present invention to provide new and improved apparatus that is not subject to the foregoing disadvantages.
It is another object of the present invention to provide an apparatus and method for enhancing the turbulent flow of particulates entrained in a transport fluid.
It is still another object of the present invention to provide an apparatus and method for substantially preventing the formation of a sheet of aggregated particulates in a centrifugal dryer against the dryer screen.
The foregoing objects of the present invention are provided generally by including a flow disrupter within the flow path of a slurry comprising a desired particulate matter and a transport fluid so as to impart a force angularly disposed to an otherwise obtained direction of travel. In a method generally in accord with the present invention a force is imparted to the desired particulate matter in an angular direction to the direction of travel. In one embodiment of the present invention, a centrifugal dryer useful for removing the transport fluid from the particulates entrained therein may include an upright, substantially cylindrical screen having a plurality of apertures sized to allow the transport fluid to flow through but not the entrained particulates. The dryer may include an inwardly directed flange that imparts a radially inward direction of force to the aggregating particulates, causing them to move radially inwardly into contact with the rotor blades, thus restoring the intended reciprocal bouncing of the particulates between the rotor and the screen.
The foregoing objects of the invention will become apparent to those skilled in the art when the following detailed description of the invention is read in conjunction with the accompanying drawings and claims. Throughout the drawings, like numerals refer to similar or identical parts.